Well site geologist Peter Thorn has seen a lot of North Sea rocks sliding under his microscope, maybe more than anyone else. Here, he reflects on his career and how the profession of a well site geologist has changed over the years.
“I never intended to join the oil and gas industry”, says Peter Thorn whilst we are being served a coffee in a café overlooking Aberdeen Harbour on a cold and crisp winter’s day.
Now, Peter is one of the most experienced well site geologists in the greater North Sea area. With more than 35 years of working both offshore and onshore behind him, sitting 100’s of wells, there are few who can claim to have more experience than him. For that reason, he has gained a strong reputation and is especially in demand when it comes to drilling HPHT wells.
“The lifestyle suits me”, he says. “Yes, being away for weeks on end has never been pleasant, but when I’m back home, my family and friends have my full attention.” He doesn’t feel that he missed on much, despite the time spent away from home.
Mining and Aberdeen
When looking at his academic years, nothing hinted towards a career in petroleum. “I came to Aberdeen to carry out a PhD, studying tungsten mines in Bolivia. I spent about a year in and around the mines, it was a fascinating time”, Peter says. Aberdeen University at the time had a strong foothold in hard rock geology.
Even when Peter joined the offshore industry as a mudlogger in 1984, he still intended to join the mining industry again, where he had also worked for a year prior to his PhD. It worked out differently.
The mining sector experienced a major slump at the time, and with oil and gas drilling booming globally as well as in the UK, it wasn’t difficult to see why the change from hard rock to soft rock was not a temporary one.
Peter Thorn in Aberdeen, with the harbour in the background. Photo: Henk Kombrink
“..samples retrieved from the shakers had a much more prominent position in the real-time interpretation process.”
The only computers on the rig
“The well site geologist and mudlogging professions have changed a lot over the decades”, Peter continues while a supply vessel slowly leaves the quay to provide supplies to one of the many platforms still out there in the North Sea.
There was a lot more geology involved in the job. “Logging while drilling wasn’t used or was very basic, so the samples retrieved from the shakers had a much more prominent position in the real-time interpretation process”, Peter explains.
“Coring also seems a thing of the past”, Peter says. “The number of meters of core I cut I don’t remember, but it’s a lot. And rather than sleeved coring, where the well site geologist often won’t see the whole core because it is hidden in an aluminium cylinder, we were also tasked with laying out the core in 1-m sections and put these into wooden boxes. We may not have done a detailed interpretation, but it was always very satisfying to see a whole core and not just rock chips. Nowadays, many geologists have never seen a coring job.”
“While oil fluorescence is fairly easy to detect using water-based muds, I’ve never been 100% convinced of oil fluorescence whilst using oil-based muds.”
Without real-time logging, it was also more challenging to discern a hydrocarbon-bearing reservoir from a water-bearing one. Especially in the case of oil-based mud, the ability to interpret a show will always be surrounded with uncertainty. “While oil fluorescence is fairly easy to detect using water-base muds, I’ve never been 100% convinced of oil fluorescence whilst using oil-based muds”, Peter says. “Connection gas and gas-readings form very important indicators, if not the most important ones,” he adds. It is an important observation, especially for the office geologist who is looking for missed pay in the right-hand column of old composite logs.
“Being a mudlogger may not be seen as the most exciting job on the rig, but it was the mudloggers and wireline engineers who were the first to get access to a computer”, Peter continues. Yet, the capabilities of these machines were very limited. “I remember witnessing my first Cement Bond Log and because the computer lacked the capability to store the generated data, the print-out of the data recorder was all we had. To put things into further context, all communication to onshore took place via Telex, a way of sending messages that the younger generation will have never come across.”
Wash the samples!
“Drilling development wells was often done without a logging unit”, Peter explains. The geology is well-known, so why kit out an entire room for a well site geologist? “It was the case at an important oil field across the North Sea, where I happened to go to many times in the past. However, even though drilling seemed straightforward, determining when the bit had entered the reservoir still required some geological input. The petroleum engineer had struggled to understand the lithologies.”
“I then suggested to wash some samples and have a quick look under the microscope. It was all that was required to make the distinction between mudstone and sandstone, and the distinction between reservoir and seal”, Peter explains. It sparked the business idea to provide a geologging service; rather than having an entire well site kit with us, we just brought a sieve and a microscope. That’s enough for many development wells.” A geologist on board can make the difference.
Interpreting rock flour
“Many things have changes over the decades”, Peter continues. “The attitude towards safety dramatically improved and communication technology enables people in the office to monitor progress real time. “Back in the days, I brought a stationary box with me offshore that contained all the data and information I needed, nowadays decisions are being made onshore as the data can be watched on mobile phones.”
“Back in the days, I brought a stationary box with me offshore that contained all the data and information I needed.”
“Drilling is also much faster,” Peter continues, “we drilled 5-10 feet per hour in the Chalk 30 years ago, now it is up to 50 feet in the same amount of time. The arrival of PDC (polycrystalline diamond compacts) bits changed our interpretation routines dramatically”, Peter further explains. This type of drill bit creates distinct PDC shaped cuttings in mudstones but typically mills the sandstones into much smaller particles, called rock flour, which can make it challenging to identify when the reservoir has been penetrated.
The major progress made in logging while drilling tools has made lithological descriptions part of a broader suite of data. However, interpreting the rocks will always remain critical. “I remember talking to a team onshore whilst we were drilling a horizontal well”, Peter recalls. “The geomodels of the engineers indicated that the well was heading towards the base of the sandstone, but I had noted that coarser-grained intervals were preferably found near the top of the sandstone, and that was what I was seeing in my samples.” A clear example of how the geology and simple observations can sometimes be so powerful.
When well-intended solutions don’t work
Peter recalls an onshore seismic wireline survey in Russia. “We needed a pit of water to put air guns in, so a hole was dug in the unconsolidated sand. As people thought it would collapse once filled with water, a wooden box was constructed, which took a few days.
It was a fine box and the guy who made it was very proud of it. The first firing of the air gun blew it to pieces, but the water-filled pit survived just long enough for the logging to be completed. The look on people’s faces was brilliant.”
An onshore seismic wireline survey in Russia. The wooden box that was carefully crafted was blown into pieces after the first firing of the air gun. Photo: Peter Thorn.
Full circle
Does Peter’s career as a whole stand for the coming and going of UK oil? He concludes: “Since the crash in 2014, my work routine has made a major shift in the sense that I had a stable and always fully booked agenda of rotations before 2014. Since then, work has been more erratic. No, I’ve never sat at home too long, I’ve been lucky, but 2014 seems to have been a watershed moment.”
“2014 seems to have been a watershed moment.”
If experienced people like Peter Thorn note a change in work routines and work availability, it is something to take seriously. Will 2014 be the year when trust and confidence in the offshore oil and gas sector has left the UK for good? Even though prices have recovered in the meantime, uncertainty in economic robustness has been replaced by uncertainty in political support.
Maybe, if Peter would have finished his PhD in mining geology in 2023, his career would indeed have continued in mining rather than oil and gas. Maybe, his career perfectly encapsulates the rise and decline of the UK’s oil and gas industry.
